1. Field of the Invention
The present invention relates to a PWM control device for PWM controlling an output current of an inverter circuit, and a motor-driven blower and an electric vacuum cleaner each equipped with an electric motor driven by the output current thereof PWM-controlled by the PWM control device. The electric vacuum cleaner described herein includes various devices, which collect various solids or fluids to a collection region through the use of negative pressure.
2. Description of the Related Art
As a conventional motor-driven blower, there has been known one having an overcurrent protecting function which determines an inrush current (overshoot current) and an unusual or improper current at its startup. In this type of motor-driven blower, a current I that flows through a brushless motor of the motor-driven blower, increases instantaneously but decreases with time upon the startup of the motor-driven blower as shown in FIG. 12. On the other hand, when the brushless motor is overloaded continuously or the motor-driven blower is brought into a locked state, an excessive current continues to flow.
Therefore, an overcurrent detected value Iz and an overcurrent detected time Tz are set and detected simultaneously. By doing so, the inrush current at the startup and the improper current can be discriminated or determined. Namely, if Tz<Tb is taken when Iz<I, then the improper current is found to have occurred and the current is interrupted. Various circuit configurations each having such a function has heretofore been proposed.
According to such means, however, a large current will flow upon the startup of the motor-driven blower while the time is exactly short, thus applying a load to each of electronic parts on an electric circuit. Therefore, there has been proposed a technology, which suppresses the inrush current at the startup as much as possible. There is known, for example, a method disclosed in Unexamined Patent Publication No. Sho 62(1987)-277877, wherein a signal having a short pulse width is outputted in a PWM inverter device only for a predetermined time upon the startup of the motor-driven blower to start up the motor-driven blower.
However, Unexamined Patent Publication No. Sho 62(1987)-277877 does not disclose any specific means for outputting the signal having the short pulse width upon the startup of the motor-driven blower.